This invention generally relates to systems and methods for ultrasonic inspection of products of manufacture. In particular, the invention relates to systems and methods for ultrasonic inspection of manufactured components immersed in an acoustic coupling medium.
Ultrasonic testing is a common method for evaluating the integrity and quality of components. This technique requires a method for coupling the ultrasonic wave energy from a transducer into the component being inspected. One way to couple the ultrasonic wave energy into the component is to immerse the component in a bath of a suitable acoustic coupling medium, such as water. This method has been used widely for inspecting aerospace components.
Ultrasonic inspection of integrated circuits, capacitors, and other electronic components has been utilized for years. In part, the broad use of this technique is based on the fact that ultrasonic inspection is non-destructive. Delaminations within the electronic components, especially integrated circuits, or other anomalies affecting internal electrical leads, are the usual subjects of this form of inspection. One hundred percent inspection is desirable because incomplete electrical connections within a component cannot be seen and may render the component unusable.
Coupling an ultrasonic wave or beam to an electronic component usually requires a liquid medium for inspection of electrical connections within that component; in air or other gaseous media, losses for the ultrasonic signal are often too great. In many known ultrasonic inspection systems the component requiring inspection is immersed in a tank of water or some other liquid coupling medium. This technique is well suited for imaging internal structures in components due to the uniform coupling of ultrasonic wave energy into the component.
Some components, due to their design and manufacture, cannot be immersed in a fluid. In particular, often it is not acceptable to get the test sample wet. For example, moisture in an electronic component could cause that component to fail in operation. The key to evaluating such an electrical component is to keep it dry.
The prior art for inspecting components that cannot come in contact with water was to paint the surfaces of the component prior to immersion inspection. This method is often undesirable. Cleaning the paint from the surfaces of the test sample, following inspection, is difficult. Paint that remains on the surface of the component may also hinder the usefulness of the component. In the case of some electrical components, the component would be damaged by contact with most fluids including paint.
Thus there is a need for a method of ultrasonic immersion inspection whereby the component being inspected is not exposed to moisture.
The present invention is directed to a technique that allows for the immersion ultrasonic inspection of test samples that cannot be immersed in a fluid (e.g., water) bath. In accordance with the preferred embodiment of the invention, a test sample is encapsulated in a vacuum bag before it is immersed in the fluid. Air will greatly affect the quality of the ultrasonic evaluation. Therefore, using a vacuum pump, the air is removed from the bag so that, when the vacuum bag is immersed in fluid, the ultrasonic wave energy can couple from the fluid through the vacuum bag into the component without traveling through an intervening air gap.
In one aspect, the invention encompasses a method for ultrasonic inspection of a test sample, comprising the steps of: enclosing a test sample within nonporous flexible material, with a portion of the nonporous flexible material being in contact with (i.e., with no air gap present} a surface area of the test sample; immersing the enclosed test sample in an acoustic coupling medium; and transmitting ultrasound wave energy from a location in the acoustic coupling medium toward the surface area of the test sample. The surface area where the ultrasound wave or beam impinges will be a function of the location of the source of the ultrasound wave energy and the location of the particular portion of the test sample being inspected.
The invention is further directed to a system for ultrasonic inspection of a test sample, comprising: a volume of an acoustic coupling medium; an enclosure made of nonporous flexible material immersed in the acoustic coupling medium; a test sample enclosed inside the enclosure with a portion of the nonporous flexible material being in contact with a surface area of the test sample; and an ultrasonic transducer immersed in the acoustic coupling medium. Optionally, the transducer can be mounted on an electromechanical scanning apparatus. The scanning apparatus may be controlled by a computer program for causing the transducer to scan the test sample along a predetermined scanning path.
In accordance with the preferred embodiments of the invention, the fluid is water, the test sample is an electrical component, and the nonporous flexible material is rubber, kapton, polyethylene or acrylic. Other nonporous flexible materials can be used provided that the material has acceptable acoustic impedance.